1. Field of the Invention
This invention relates to a mold assembly for molding an elastomeric sealing member to an annular seal case so as to form a shaft seal.
2. Description of Prior Developments
Prior mold cavities are often defined by a stationary mold member and two concentrically arranged movable mold members. The movable mold members are typically located above the stationary mold member for coordinated downward motions. The outer movable mold member is initially moved downwardly against the stationary mold member to establish the mold cavity contour and later prevent the movement of mold flash in an outward radial direction.
The inner movable mold member is subsequently moved downwardly to compress a charge of elastomeric molding material that is pre-positioned on an annular shelf provided by the stationary mold member. The molding material is thereby pumped or squeezed radially outwardly from the shelf into the mold cavity defined by the outer mold member.
These movable mold members are commonly driven toward the stationary mold member by means of heavy duty disk springs that act in a sequential fashion so that the outer movable mold member is in its final position before the inner movable mold member begins to exert a squeezing force on the charge of molding material. The heavy duty springs provide the required spring force to prevent the mold members from separating under the hydrostatic molding pressure. This high spring clamping force necessitates a significant spring stack height. Moreover, a large spring stack height is needed in order to provide the necessary axial travel and clearance between the sequentially movable mold members and the fixed mold members.
Some older presses still in use do not have the necessary axial clearance or axial closed height to be able to utilize the described mold member assemblies. That is, the axial extent of the mold members and spring stacks is greater than the closed height of these molds. Since many older presses operate with a fixed cam-driven stroke, modern mold assemblies having considerable axial length would interfere with press closure.
U.S. Pat. No. 3,950,119 is representative of the prior art insofar as it shows a stationary lower mold member and two concentrically arranged upper mold members. The outer upper mold member forms the upper surface contour of the mold cavity and the inner upper mold member acts as a pumping device to pump the elastomeric molding material radially outwardly into the mold cavity. Each of the upper mold members has a resilient drive connection with the upper press element in the form of multiple stacks of disk springs or Belleville washers.
U.S. Pat. No. 4,249,874 shows an arrangement that is generally similar to the arrangement depicted in U.S. Pat. No. 3,950,119, as regards the above-noted features. U.S. Pat. No. 4,824,357 shows a variation of the above-noted arrangement wherein a single upper mold member is cooperatively associated with two lower mold members. Each of the lower mold members is biased upwardly by means of a stack of spring disks.
U.S. Pat. No. 4,555,376 shows a molding assembly wherein an inner annular clamping member is biased downwardly by a spring system so as to hold a polytetrafluoroethylene disk in a fixed position on the lower mold member. Subsequently, an outer mold member is driven downwardly to engage a metal seal case, thereby closing the mold cavity. The downward motion of the outer mold member is continued so as to deform the metal case and reform the elastomeric molding material to the dimensions of the closed mold cavity.
The present invention is concerned with an axially compact mold member assembly wherein a single movable mold member is used to both compress and mold the elastomeric molding material. The single movable mold member has a rigid, non-resilient connection with the associated press such that the mold member assembly has a relatively short height in its closed position so that it can be used with older presses.
The mold member assembly of the present invention does not utilize multiple stacks of heavy duty springs disposed in an axially tandem relationship with movable mold cavity members, such as are used in relevant prior arrangements. The spring stack of the present invention is removed from contact with the movable mold cavity forming members and arranged radially outwardly therefrom. In this manner, the spring stack is axially coextensive with the movable mold members.
Since no spring stack is provided over or under the movable mold members, the axial height of the mold may be reduced by the amount equal to that which would have been required to accommodate the spring stack. A principal advantage of the invention is that the mold member assembly can be mounted in older presses having relatively short mold member clearance spaces between the upper and lower mold shoes.